Modern internal combustion engines generate hydrocarbon emissions by evaporation of combustible fuels such as gasoline. As a result, vehicle fuel vapor emissions to the atmosphere are regulated. For the purpose of preventing fuel vapor from escaping to the atmosphere, an evaporative emissions control (EVAP) system is typically implemented to store and subsequently dispose of fuel vapor emissions.
The EVAP system is typically designed to collect vapors produced inside an engine's fuel system and then send the vapors through the engine intake manifold into its combustion chamber to be burned as part of the aggregate fuel-air charge. When pressure builds inside the fuel tank as a result of evaporation, fuel vapors are transferred to and stored in a carbon canister. Subsequently, when engine operating conditions are conducive, a valve is opened and vacuum from the intake manifold draws a purge flow of the stored hydrocarbons from the canister to the engine's combustion chamber. Thereafter, the carbon canister is regenerated with newly formed fuel vapor, and the cycle can continue.
In naturally aspirated engines, the intake manifold provides the vacuum required for the purge flow. In conventional forced induction engines, the intake manifold can be used for purge flow when under vacuum, but in boosted modes the purge flow must be achieved through a secondary vacuum source. This is typically accomplished using a purge ejector tee or jet pump having a venturi to create a vacuum and pull the fuel vapor from the canister using boost pressure. However, such systems require additional parts that increase cost and may become disconnected, thereby requiring complex leak detection systems. Accordingly, while such systems work well for their intended purpose, there remains a need for an improved EVAP system.